The invention relates to a filter especially for the combustion air for internal combustion engines.
U.S. Pat. No. 4,720,292 discloses an air filter with the following features,
A housing is provided with an axial outlet opening and a substantially open second end which can be closed by a removable cover. An air inlet opening is provided on the periphery of the housing. In the housing there is a substantially cylindrical filter element with an internal support tube, and a filter with an external support tube, the inner filter element being disposed coaxially in the housing. The sealing of the filter element to the housing is provided by an annular end plate which has a substantially cylindrical surface directed radially inward and is pushed over an inner section of the outlet portion.
As is well known, the filter inserts of air filters are replaced after a certain period of operation. Depending on the amount of dust in the air, the useful life of an air filter may amount to a few daysxe2x80x94in construction machines, for examplexe2x80x94to several months. The filter insert disclosed in the above referenced filter insert, as well as others commonly used filter inserts, consist of a combination of materials, especially using sheet steel for the support tubes. The filter medium is paper or a synthetic nonwoven material, and the end plates consist of synthetic resin (soft elastomer). The disposal of such air filters or their breakdown into their individual component materials entails great expense and has therefore been uneconomical.
Basically, the avoidance of waste takes precedence over waste recycling and disposal. For the process of recycling, such recycling must be industrially possible, its cost must be reasonable, and a market must be able to exist or be created for the resultant material or energy. Not until these criteria are met can wastes be properly disposed of.
In the case of air filter inserts, recycling has thus far been impossible on account of the above-described disadvantages.
Another disadvantage of the known state of the art is to be seen in the fact that a relatively large housing is required for the air filter insert, which demands an unnecessarily great amount of space in the clean air area.
It is therefore the object of the invention to provide a filter of metal-free design, which can be disposed of without difficulty and has a very compact construction. This object is achieved by the invention as described and claimed hereinafter.
The core idea of the invention lies in the use of a material that is outstandingly suitable for the end plates of an air filter and thoroughly suitable for combining a filter medium with support structures. One such material is, for example, a thermoplastic elastomer, (or) especially a thermoplastic polyurethane.
Thermoplastic elastomers are materials in which elastomeric phases are bound as soft components into plastics as hard components. Unlike elastomers, thermoplastic elastomers, abbreviated TPE, are crosslinked, not chemically irreversibly but physically reversibly. The reversible crosslinking is produced by their biphasic structure. If the molecular architecture is suitable, the domains of the hard sequences form the physical crosslinking points in a continuous matrix of the soft sequences, which at the same time are selected such that, at the temperature of their use, they are above their glass temperature (freezing temperature). The glass transition temperature (if amorphous) or the melting temperature (if partially crystalline) of the hard sequences must, however, be above the temperatures of use, and thus the domains of the hard sequences can act as crosslinking points. TPE""s therefore behave at the temperature of use like elastomers, but above the characteristic equilibrium temperature the hard sequences become mobile and the thermoplastic elastomers can then be worked like thermoplastics.
The great advantage of TPE over vulcanized elastomers lies in its substantially simpler processing which eliminates mastication (oxidative degradation), the admixture of vulcanization accelerators, and in some cases even the compounding, and also, of course, vulcanization.
The thermoplastic polyurethanes are, like all plastics of this family, polyaddition products of polyisocyanates and polyols. Their rubber-like behavior results from the segment-like structure of the macromolecules. Here too a hard segment is combined with a soft segment the thermoplastic polyurethanes are characterized by high flexibility even at low temperatures, durability at high temperatures, great resistance to tearing, great vibration damping ability, and high resistance to fats, oils and solvents, as well as to high-energy radiation and ultraviolet light.
The polar-structure thermoplastic polyurethane resin elastomers can be mixed with other thermoplastics and fabricated together with them.
A further refinement of the invention envisions additionally providing the filter medium with support bodies which can surround the filter medium and thus improve its stability.
In an additional embodiment of the invention at least one end plate is equipped with a sealing system; these end plates can have both an axially directed and a radially directed sealing structure. Preferably the end plate is provided with a concentric collar bearing a radial gasket. Fundamentally it is possible to equip the elements consisting of thermoplastic elastomer or thermoplastic polyurethane with functional structures. Thus, for example, an end plate can be provided with support bodies or with connecting elements.
In a process for the production of the air filter, first a hollow cylindrical pleated element is prepared from a filter medium. The end plates are fused onto the axial end faces of the filter insert with, for example, high-temperature heating elements and bonded to the filter medium. Instead of fusing them with hightemperature temperature heating elements, mirror welding can also be used.